In order to understand the mechanics of ultrasound, we first need to have a basic knowledge of sound waves, how they are generated and how they travel through a conductor. The dictionary defines sound as the transmission of vibration through an elastic means that may be solid, liquid or gaseous. Sound wave generation – a sound wave is produced when a single or repetitive movement is generated in a sound conductor, such as through a shock or a vibrating movement. The movement of air through the cone of a radio loudspeaker is a good example of vibratory sound waves generated by mechanical movement. Since the loudspeaker cone moves forwards and backwards, the air in front of the cone is alternately compressed and rarefied in order to produce sound waves, which travel through the air until they are dispersed. The sound waves produced by alternating mechanical movement are probably more familiar to us. There are also sound waves created by a single shock event. One example is thunder, which is generated when the air instantaneously changes volume as the result of an electrical discharge (lightening). Another example of shock sounds could be the sound created when a piece of wood falls on a concrete floors. Shock events are sources of a single compressed wave that radiates out from its source.